The present invention relates generally to a fault locating system for locating a fault in a power distribution system, and more particularly to an improved method and apparatus for locating a fault in an underground power distribution system, such as may be used in residential or urban settings.
Other fault locating systems have been used to locate faults in overhead power distribution systems. Overhead power distribution systems are typically used in rural settings, and, less frequently today than in the past, in residential and urban settings. Overhead distribution systems typically have fused cutout switches mounted on power distribution poles at various locations along a given distribution line. Often the cutout switches incorporate a current limiting fuse. When a fault occurs in the overhead distribution system, the fused cutout switch in series with the fault typically blows open. The line crew may visually inspect the faulted line from a repair vehicle, and locate the faulted portion of the line when the open cutout switch is seen. The faulted portion of the line is then isolated from the balance of the power system for repair.
Underground power distribution systems are not as easily inspected as overhead distribution systems because the majority of the components are located beneath ground level. Some of the underground power distribution system components are located above ground, such as fused switchgear, but the above-ground components are supplied as a totally enclosed pad mounted unit. Furthermore, the extensive use of underground power distribution systems is a more recent development, that is, for many years the vast majority of power distribution systems have been overhead systems.
An earlier known method to locate a fault in an underground distribution power system uses a trial and error trouble shooting process. Using this known method (described in further detail below) the upstream power consumers or customers, that is the customers between the fault and the substation, continually experience intermittent power outages followed by voltage spikes upon re-energization of the line. This earlier method is a particular inconvenience and disruption for upstream customers running computers and other high technology devices on line power. Thus, the upstream customers are hampered and may suffer damage as a result of any lack of reliability of the utility's power distribution system.
Known methods of trouble shooting underground distribution systems to locate a fault impose significant safety hazards on line crew personnel. In an underground vault, the suspect power lines, that is those lines suspected of having the fault, are each disconnected and the blown switchgear fuses are replaced. The suspect power lines are manually reenergized one at a time using a hot stick. Upon reenergizing the faulted line, arcing flashovers and ensuing vault fires may occur. The danger of flashover, and resulting injury to one's eyes if viewed, leads to the practice of the line crew member facing away from the vault and pushing backward on the hot stick to reconnect each suspect line. If a vault fire should occur, it does so behind the line crew member's back, which may delay a reaction to move to safety. Beyond the danger to line crew personnel, a vault fire can significantly damage the connecters, cables, and any other equipment in and around the vault.
Thus, a need exists for an improved underground power line fault locating method and apparatus, such as may be used in residential settings, which is not susceptible to the above limitations and disadvantages.